The loss and degradation of prairie-oak ecosystems in the southern Puget Lowland and northern Willamette Valley ecoregions of western Washington State have contributed to population declines of many avian species, including the slender-billed white-breasted nuthatch (Sitta carolinensis aculeata). The nuthatch, a cavity-nester and near-obligate of Garry oak (Quercus garryana) habitats, was once considered a common resident. More recently, nuthatches were considered primarily restricted to the northern Willamette Valley ecoregion and extirpated from the northern part of their range, although information on abundance, distribution, and habitat association was limited. To address this, we conducted roadside and off-road point count surveys and collected habitat data across their historical range. In 2024–2025 we surveyed nuthatches and measured habitat at 479 locations during the breeding season, recording 100 nuthatch detections at 80 points. Most detections occurred in the northern Willamette Valley ecoregion where relative abundance was much higher (0.48 birds/point) than in the southern Puget Lowland ecoregion (0.09 birds/point). Survey points with nuthatch detections contained more large (45–60 cm dbh) and fewer small (10–30 cm dbh) Garry oak trees and had oak canopies that were higher and denser. Our findings indicate that nuthatches are more abundant and widely distributed in western Washington than previously believed, including apparent recolonization of areas where they were considered extirpated. However, the subspecies remains rare and at risk. Information here will help inform land-management practices that contribute to slender-billed white-breasted nuthatch conservation throughout western Washington.
Cascadia Prairie-Oak Partnership
Providing coordination for the technical prairie community in the Willamette Valley, Puget Trough, Georgia Basin (WPG) ecoregion and beyond.